Study On Modeling And Analysis Of Hybrid Batch/Continuous Processes Using Hybrid Petri Nets

Hybrid systems are composed of discrete event dynamic systems and continuous time dynamic systems, which interact with each other. The hybrid system theory, proposed on the demand of the economic development, is the result of the development of computer science and control theory. As a typical hybrid system, hybrid batch/continuous processes are one of the most impotant processing modes in the process industries. The behaviors of this kind of process can no longer be considered as either continuous or discrete, and therefore pose a difficult problem with regards to formulation and solution algorithm. Modeling and analysis of hybrid batch/continuous processes using hybrid petri nets model was developed in this paper. This work was supported by the National Natural Science Foundation of China (grant No.60243002), and the Natural Science Foundation of GuangXi (grant No. GuiKeQing 0640032). This paper makes following contributions:(1) On the view that the dynamics of time Petri nets can also be approximated continuously, a general continuous Petri nets (CPNs) formalism----Interval speed CPNs) was considered. The problem of behavior analysis and effective conflict for interval speed continuous Petri nets (ICPNs) was developed, and the necessary and sufficient condition for a steady state to be reachable was presented. (2) As the traditional algorithm for the dynamic evolution of Hybrid Petri Nets may not be used for many HPNs models, a new algorithm to construct evolution graph for HPNs was developed. Through case study, the effectiveness of the developed algorithm was illustrated. (3) The decidability of marking rechability for hybrid Petri nets was discussed. The necessary and sufficient condition for a marking to be reachable was presented. Also, an algorithm that decides whether a given marking is reachable or not was introduced through the evolution graph of HPNs. (4) A p-time Petri nets-based formulation approach for batch plants with complicated intermediate storage policies (such as: unlimited intermediate storage, no intermediate storage, finite intermediate storage, and mixed intermediate storage) was presented, then an algorithm for short-term scheduling of batch plants based on a feasible schedule set and a modified branch & bound is developed. In this method, the condition that the minimal makespan of one batch no greater than the minimal makespan of the other batch was presented, thereby the explicit enumeration of search was avoided so that the algorithm performance was improved. Through case study, the effectiveness of the proposed approach and algorithm are illustrated. (5) A new type of hybrid Petri nets model called general hybrid Petri nets (GHPNs) is defined. The enabling and firing semantics of transitions of the GHPNs is discussed, and the net dynamic behavior is also developed. As an example of application, we show how the proposed formalism can be applied to modeling and optimization of a flexible manufacturing system. (6) Motivated by the need of the effective scheduling and control of operations in sugar milling, hybrid time Petri nets(HTPNs) which allows the formulation of variable cycle time and variable flow rate in sugar milling systems was considered. Through analysis of HTPNs model, an effective scheduling algorithm for sugar milling systems was developed. (7) To analyze Fluid Stochastic Petri nets(FSPN) model by First-Order Hybrid Petri Nets(FOHPN) model, the formal conversion from Fluid Stochastic Petri nets to First-Order Hybrid Petri Nets was presented. Also, the effectiveness of the proposed conversion was proofed.Through case study, the necessity of the conversion is illustrated.